“Why shouldn’t a mother marry her daughter? Why shouldn’t two elderly sisters living together marry each other?”

He added: “When we have a queen who is a lesbian and she marries another lady and then decides she would like to have a child and someone donates sperm and she gives birth to a child, is that child heir to the throne?

Our incest laws would stop a mother marrying her daughter for tax or any other purposes and Lord Tebbit’s crazy rants will undoubtedly put his son off consummating their marriage. I would also assume that if we had a lesbian queen who gave birth to a child, that child would be heir to the throne.

Others retort that ‘gay marriage is a stepping stone to the legalisation of bestiality’. Remember when giving women the vote meant that the government also had to give horses the right to vote? No, because that never happened. Why would giving gay people the right marry lead to others being able to marry their pets? It’s just as irrational.